In recent years, electronic devices have been down sized and yet equipped with more functions, which demands the electronic components employed in those devices to be smaller in size. Torque of a rotary-type-electronic-component, in general, decreases at the smaller size of the component while the structure thereof is maintained. This drawback has been overcome, and downsized rotary type electronic components with given torque are prevailing in the market.
A rotary type encoder, as an example of the conventional rotary type electronic component, is described hereinafter with reference to FIGS. 4 and 5.
FIG. 4 is a side sectional view of a conventional high-torque rotary encoder, and FIG. 5 is an exploded perspective view of the same.
In FIGS. 4 and 5, rotary shaft 510 is made of resin, and its upper section works as an operating section 511. A lower section of shaft 510 has flange 512 formed integratively therewith. A mid section of shaft 510 forms cylindrical shaft 513 journaled by through-hole 521 boring in metal bearing 520. Grease of high viscosity is applied to the journaling section.
Beneath bearing 520, flange 512 and box-type case 530 made of resin are situated in tandem. Beneath the center of flange 512, positioning section 514 is provided, which is inserted into hole 531 provided on case 530 so that shaft 510 is jounraled by case 530.
Beneath flange 512, movable contact 540 made of resilient metal leaf is mounted. Movable contact 540 elastically contact to fixed contact 550 formed by contacts forming in radial on recessed base of case 530. Both the contacts form a contact section for producing pulse signals. Terminal 560 electrically conductive to fixed contact 550 extends outside case 530 from a side of case 530. Contact 540, 550 and terminal 560 form electric-signal-producing-section 570.
Metal cover 580 covers periphery of the base of bearing 520 and locks case 530. Between cover 580 and an upper face of case 530, a frame of spring 590 made of resilient metal leaf is rested. Resilient leg section 591 of spring 590 elastically contacts on step 515 of flange 512.
An operation of the rotary encoder constructed above is described as follows:
When operating section 511 of shaft 510 is rotated, flange 512 rotates accordingly. Then movable contact 540 elastically slides on fixed contact 550, thereby producing a pulse signal as a given electric signal. The pulse signal is taken out from a plurality of terminals 560.
Resilient leg 591 of spring 590 urges downwardly step 515 of flange 512 so that step 515 rotates. Shaft 510 thus obtains predetermined torque.
As discussed above, the conventional encoder is constructed such that shaft 510 can obtain high torque by urging elastically leg section 591 against step 515.
However, according to this construction, the outer diameter of leg section 591 of spring 590 is obliged to decrease at the narrower diameter of the electronic component, which weakens the urging force of leg section 591. In order to overcome this drawback, it is a general method that the elastic urging force of spring 590 is boosted considering the material and leaf thickness of spring 590. This method still has some limit, and if a greater urging-force of the spring can be produced, it would apply an intensive pressure to a local point on flange 512 where spring 590 urges. Even if grease is applied to the contact face, tactile feel at operating becomes worse, and the frictional faces are heavily worn out.